The invention relates to a method for hydrolyzing hydrolyzable metallic salts with emulsions of water and inert liquid.
In the reaction of chlorosilanes of metallurgical silicon and HCl gas to give trichlorosilane (TCS) and silicon tetrachloride (STC), which are used, for example, as raw materials for the production of semiconductor-pure silicon, solar silicon and highly disperse silicic acid, metallic salts, mainly metallic chlorides, are formed as by-products. In particular, aluminum chloride and iron chloride deposit as a solid on cooling the reaction mixture. Selective deposition of the solids is important in terms of process technology in order to avoid changes in the distillative work-up of the liquid silanes. Various methods are known for the separation of the solid metallic chlorides from the process.
In DE 2623290 A1, the deposition of AlCl3, mixed with FeCl3 from the gaseous reaction mixture of chlorosilanes in Liebig tubes, is described. The cleaning of the Liebig tubes is not described.
Since the solids are generally mixtures of highly corrosive compounds, the immediately subsequent hydrolysis and optionally neutralization of the resulting aqueous solutions is preferred to a purification of the solids (for utilization). In the hydrolysis of the anhydrous metallic chlorides (in particular of the main constituent aluminum chloride), as is known a very high quantity of heat is released, which in the case of inadequate heat dissipation can lead to the evaporation of the water and as a result to uncontrolled pressure build-up and thus to dangerous plant conditions as far as to explosion.
For safety reasons, apparatus and plant components that are contaminated with these metallic chlorides are therefore dismantled for cleaning by hydrolysis. In addition to the danger of an accident on opening the plant and transport of the contaminated apparatus, this causes a high logistic complexity in order to avoid downtimes. The safety risks associated therewith and the cost are considerable.
As an alternative, for example, a method is described in EP 1174388 A1 in which the metallic chlorides are laboriously filtered off after precipitation in a quencher and thus isolated in utilizable form. Since generally, however, mixtures of metallic chlorides are concerned, here also the hydrolysis and subsequent disposal by means of a waste-water treatment plant is economically more advantageous than a further laborious purification. The hydrolysis can then be controlled by means of the feed rate of the filter cake.
The object was to hydrolyze solid hydrolyzable metallic salts in a simple and hazardless manner.